II-VI/III-V layered construction on InP substrate

ABSTRACT

A layered construction is provided comprising an InP substrate and alternating layers of II-VI and III-V materials. The alternating layers of II-VI and III-V materials are typically lattice-matched or pseudomorphic to the InP substrate. Typically the II-VI material is selected from the group consisting of ZnSe, CdSe, BeSe, MgSe, ZnTe, CdTe, BeTe, MgTe, ZnS, CdS, BeS, MgS and alloys thereof, more typically selected from the group consisting of CdZnSe, CdMgZnSe, BeZnTe, and BeMgZnTe alloys, and is most typically Cd x Zn 1−x Se where x is between 0.47 and 0.57. Typically the III-V material is selected from the group consisting of InAs, AlAs, GaAs, InP, AlP, GaP, InSb, AlSb, GaSb, and alloys thereof, more typically selected from the group consisting of InP, InAlAs, GaInAs, AlInGaAs and GaInAsP alloys, and is most typically InP or In y Al 1−y As where y is between 0.47 and 0.57. In one embodiment, the layered construction forms one or more distributed Bragg reflectors (DBR&#39;s). In another aspect, the present invention provides a layered construction comprising: an InP substrate and a distributed Bragg reflector (DBR) having a reflectivity of 95% or greater which comprises no more than 15 layer pairs of epitaxial semiconductor materials. In another aspect, the present invention provides a laser comprising a layered construction according to the present invention. In another aspect, the present invention provides a photodetector comprising a layered construction according to the present invention.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.10/871,424, filed Jun. 18, 2004, now pending.

FIELD OF THE INVENTION

This invention relates to devices, such as lasers or photodetectors,including Vertical Cavity Surface Emitting Lasers (VCSEL's), comprisingan InP substrate and alternating layers of II-VI and III-V materialswhich typically form a Distributed Bragg Reflector (DBR).

BACKGROUND OF THE INVENTION

Japanese Unexamined Patent Application (Kokai) 2003-124508 purports toclaim light-emitting diodes having AlGaInP-type light-emitting layers.(Claims 1–8). The reference emphasizes the “grid-matching” of layerswith a GaAs substrate at paragraphs 2, 15 and 21 and at claim 1. Thereference purports to claim light-emitting diodes with AlGaInP-typelight-emitting layers that contain DBR layers having a structurecomprising laminated pairs of Group II-VI material layers andAlGaAs-type or AlGaInP-type material layers. (Claims 2–4). The referencepurportedly discloses light-emitting diodes with AlGaInP-typelight-emitting layers that contain GaAlAs/ZnSe DBR layers (FIGS. 1–3,reference number 2, and accompanying description) on a GaAs substrate,and optionally a second DBR layer which is a GaAlAs/AlAs DBR layer (FIG.3, reference number 10, and accompanying description).

U.S. Pat. No. 5,206,871 purportedly discloses a VCSEL comprising mirrorscomprising alternating layers of GaP or ZnS and layers of borosilicateglass, CaF2, MgF2 or NaF.

U.S. Pat. No. 5,732,103 purportedly discloses a VCSEL comprising an InPsubstrate and lattice-matched mirror stacks comprising alternatinglayers of II-VI materials, in particular ZnCdSe/MgZnCdSe.

U.S. Pat. No. 5,956,362 purportedly discloses a VCSEL.

International Patent Publication No. WO 02/089268 A2 purportedlydiscloses high contrast reflective mirrors for use in VCSEL's whichcomprise oxide materials.

SUMMARY OF THE INVENTION

Briefly, the present invention provides a layered constructioncomprising an InP substrate and alternating layers of II-VI and III-Vmaterials. The alternating layers of II-VI and III-V materials aretypically lattice-matched or pseudomorphic to the InP substrate.Typically the II-VI material is selected from the group consisting ofZnSe, CdSe, BeSe, MgSe, ZnTe, CdTe, BeTe, MgTe, ZnS, CdS, BeS, MgS andalloys thereof, more typically selected from the group consisting ofCdZnSe, CdMgZnSe, BeZnTe, and BeMgZnTe alloys, and is most typicallyCd_(x)Zn_(1−x)Se where x is between 0.47 and 0.57. Typically the III-Vmaterial is selected from the group consisting of InAs, AlAs, GaAs, InP,AlP, GaP, InSb, AlSb, GaSb, and alloys thereof, more typically selectedfrom the group consisting of InP, InAlAs, GaInAs, AlInGaAs and GaInAsPalloys, and is most typically InP or In_(y)Al_(1−y)As where y is between0.47 and 0.57. One of the alternating layers of II-VI and III-Vmaterials may be in direct contact with the InP substrate, or additionallayers may be interposed between the alternating layers of II-VI andIII-V materials and the InP substrate. In one embodiment, the layeredconstruction forms one or more distributed Bragg reflectors (DBR's).Typically, such a DBR can be made with no more than 20 pairs ofalternating layers of II-VI and III-V materials, and more typically nomore than 15 pairs. Typically the layers of II-VI and III-V materialshave an average thickness of between about 100 nm and about 200 nm.

In another aspect, the present invention provides a layered constructioncomprising: an InP substrate and a distributed Bragg reflector (DBR)having a reflectivity of 95% or greater which comprises no more than 15layer pairs of epitaxial semiconductor materials.

In another aspect, the present invention provides a laser comprising alayered construction according to the present invention.

In another aspect, the present invention provides a photodetectorcomprising a layered construction according to the present invention.

In this application:

“lattice-matched” means, with reference to two crystalline materials,such as an epitaxial film on a substrate, that each material taken inisolation has a lattice constant, and that these lattice constants aresubstantially equal, typically not more than 0.2% different from eachother, more typically not more than 0.1% different from each other, andmost typically not more than 0.01% different from each other; and

“pseudomorphic” means, with reference to a first crystalline layer ofgiven thickness and a second crystalline layer, such as an epitaxialfilm and a substrate, that each layer taken in isolation has a latticeconstant, and that these lattice constants are sufficiently similar sothat the first layer, in the given thickness, can adopt the latticespacing of the second layer in the plane of the layer substantiallywithout misfit defects.

It is an advantage of the present invention to provide a layeredconstruction that can serve as a high reflectivity DBR for use in longwavelength InP devices such as lasers or photodetectors, includingVCSEL's, and, in particular, one that can achieve suitably highreflectivity with relatively few layers.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic depiction of a layered construction according tothe present invention which is a DBR.

FIG. 2 is a scanning electron micrograph of a cross-section of a layeredconstruction according to the present invention.

FIG. 3 is a graph of reflectivity vs. wavelength as measured for the2-pair CdZnSe/InAlAs DBR according to the present invention described inthe Example below (trace A). FIG. 3 also presents simulated reflectivitydata for the 2-pair CdZnSe/InAlAs DBR according to the present invention(trace B). FIG. 3 also presents simulated reflectivity data for twocomparative III-V/III-V DBR's: a 2-pair InGaAsP/InP DBR (trace C) and a2-pair AlGaAsSb/AlAsSb DBR (trace D).

FIG. 4 is a schematic depiction of the inventive layered constructionhaving 15 pairs of alternating layers of II-IV and III-V materials.

FIG. 5 is a schematic depiction of a photodetector of the presentinvention.

DETAILED DESCRIPTION

Briefly, the present invention provides a layered constructioncomprising an InP substrate and alternating layers of II-VI and III-Vmaterials. The alternating layers of II-VI and III-V materials aretypically lattice-matched or pseudomorphic to the InP substrate.

Any suitable II-VI materials may be used in the practice of the presentinvention. Typically the II-VI material is selected from the groupconsisting of ZnSe, CdSe, BeSe, MgSe, ZnTe, CdTe, BeTe, MgTe, ZnS, CdS,BeS, MgS and alloys thereof. Suitable alloys typically include 1–4different Group II materials and 1–3 different Group VI materials, moretypically 1–3 different Group II materials and 1–2 different Group VImaterials. Suitable alloys may include those according to the formula M¹_(n)M² _((1−n))M³ _(p)M⁴ _((1−p)), where M¹ and M² are independentlyselected from Zn, Cd, Be and Mg; M³ and M⁴ are independently selectedfrom Se, Te, and S; where n is any number between 0 and 1; where p isany number between 0 and 1. Suitable alloys may include those accordingto the formula M⁵ _(q)M⁶ _((1−q))M⁷, where M⁵ and M⁶ are independentlyselected from Zn, Cd, Be and Mg; M⁷ is selected from Se, Te, and S; andwhere q is any number between 0 and 1. In the preceding formulas, n, pand q are typically chosen so as to provide an alloy that islattice-matched or pseudomorphic to InP. In one embodiment, the latticeconstant of the alloy is estimated by linear interpolation from thelattice constants of the binary constituents of the alloy in order tofind alloy compositions that are lattice matched or pseudomorphic toInP. More typically the II-VI material is selected from the groupconsisting of CdZnSe, CdMgZnSe, BeZnTe, BeMgZnTe, and most typicallyCd_(x)Zn_(1−x)Se where x is between 0.47 and 0.57. The II-VI materialmay be n-doped, p-doped, or undoped by any suitable method or byinclusion of any suitable dopant, including chlorine or nitrogen doping.

Any suitable III-V materials may be used in the practice of the presentinvention. Typically the III-V material is selected from the groupconsisting of InAs, AlAs, GaAs, InP, AlP, GaP, InSb, AlSb, GaSb, andalloys thereof. Suitable alloys typically include 1–3 different GroupIII materials and 1–3 different Group V materials, more typically 1–2different Group V materials. Suitable alloys may include those accordingto the formula M⁸ _(r)M⁹ _((1−r))M¹⁰ _(s)M¹¹ _((1−s)), where M⁸ and M⁹are independently selected from In, Al and Ga; M¹⁰ and M¹¹ areindependently selected from As, P, and Sb; where r is any number between0 and 1; where s is any number between 0 and 1. Suitable alloys mayinclude those according to the formula M¹² _(t)M¹³ _((1−t))M¹⁴, whereM¹² and M¹³ are independently selected from In, Al and Ga; M¹⁴ isselected from As, P, and Sb; and where t is any number between 0 and 1.In the preceding formulas, r, s and t are typically chosen so as toprovide an alloy that is lattice-matched or pseudomorphic to InP. In oneembodiment, the lattice constant of the alloy is estimated by linearinterpolation from the lattice constants of the binary constituents ofthe alloy in order to find alloy compositions that are lattice matchedor pseudomorphic to InP. More typically the III-V material is selectedfrom the group consisting of InP, InAlAs, GaInAs, AlInGaAs, GaInAsP, andmost typically InP or In_(y)A1 _(1−y)As where y is between 0.47 and0.57. The III-V material may be n-doped, p-doped, or undoped by anysuitable method or by inclusion of any suitable dopant.

In an embodiment, the layered construction includes II-VI layersincluding BeZnTe or BeMgZnTe and III-V layers including InAlAs orAlInGaAs. For example, the II-VI layer can include BeZnTe and the III-Vlayer can include InAlAs; the II-VI layer can include BeZnTe and theIII-V layer can include AlInGaAs; the II-VI layer can include BeMgZnTeand the III-V layer can include InAlAs; or the II-VI layer can includeBeMgZnTe and the III-V layer can include AlInGaAs. Such an embodimentcan be doped to provide layered constructions with p-type conductivity.For example, BeZnTe can be doped with N and/or the InAlAs can be dopedwith Be. Such doping can provide low electrical resistance suitable, forexample, for use in laser diodes or photodiodes.

In an embodiment, the layered construction includes II-VI layersincluding CdZnSe or CdMgZnSe and III-V layers including InAlAs orAlInGaAs. For example, the II-VI layer can include CdZnSe and the III-Vlayer can include InAlAs; the II-VI layer can include CdZnSe and theIII-V layer can include AlInGaAs; the II-VI layer can include CdMgZnSeand the III-V layer can include InAlAs; or the II-VI layer can includeCdMgZnSe and the III-V layer can include AlInGaAs. Such an embodimentcan be doped to provide layered constructions with n-type conductivity.For example, CdZnSe can be doped with Cl and/or the InAlAs can be dopedwith Si. Such doping can provide low electrical resistance suitable, forexample, for use in laser diodes or photodiodes.

In an embodiment, the layered construction includes II-VI layersincluding ZnSeTe and III-V layers including InAlAs or AlInGaAs. Forexample, the II-VI layer can include ZnSeTe and the III-V layer caninclude InAlAs or the II-VI layer can include ZnSeTe and the III-V layercan include AlInGaAs. Such an embodiment can be doped to provide layeredconstructions with p-type or n-type conductivity. For example, theZnSeTe can be doped with Cl to provide n-type conductivity or with N toprovide p-type conductivity and/or the InAlAs can be doped with Si toprovide n-type conductivity or with Be to provide p-type conductivity.Such doping can provide low electrical resistance suitable, for example,for use in laser diodes or photodiodes.

In an embodiment, the II-VI material includes ZnSe or an alloy thereof,and the III-V material includes InAs, AlAs, GaAs, InP, AlP, GaP, InSb,AlSb, GaSb, or an alloy thereof. In an embodiment, the II-VI materialincludes CdSe or an alloy thereof, and the III-V material includes InAs,AlAs, GaAs, InP, AlP, GaP, InSb, AlSb, GaSb, or an alloy thereof In anembodiment, the II-VI material includes BeSe or an alloy thereof, andthe III-V material includes InAs, AlAs, GaAs, InP, AlP, GaP, InSb, AlSb,GaSb, or an alloy thereof In an embodiment, the II-VI material includesMgSe or an alloy thereof, and the III-V material includes InAs, AlAs,GaAs, InP, AlP, GaP, InSb, AlSb, GaSb, or an alloy thereof In anembodiment, the II-VI material includes ZnTe or an alloy thereof, andthe III-V material includes InAs, AlAs, GaAs, InP, AlP, GaP, InSb, AlSb,GaSb, or an alloy thereof In an embodiment, the II-VI material includesCdTe or an alloy thereof, and the III-V material includes InAs, AlAs,GaAs, InP, AlP, GaP, InSb, AlSb, GaSb, or an alloy thereof In anembodiment, the II-VI material includes BeTe or an alloy thereof, andthe III-V material includes InAs, AlAs, GaAs, InP, AlP, GaP, InSb, AlSb,GaSb, or an alloy thereof In an embodiment, the II-VI material includesMgTe or an alloy thereof, and the III-V material includes InAs, AlAs,GaAs, InP, AlP, GaP, InSb, AlSb, GaSb, or an alloy thereof In anembodiment, the II-VI material includes ZnS or an alloy thereof, and theIII-V material includes InAs, AlAs, GaAs, InP, AlP, GaP, InSb, AlSb,GaSb, or an alloy thereof In an embodiment, the II-VI material includesCdS or an alloy thereof, and the III-V material includes InAs, AlAs,GaAs, InP, AlP, GaP, InSb, AlSb, GaSb, or an alloy thereof In anembodiment, the II-VI material includes BeS or an alloy thereof, and theIII-V material includes InAs, AlAs, GaAs, InP, AlP, GaP, InSb, AlSb,GaSb, or an alloy thereof. In an embodiment, the II-VI material includesMgS or an alloy thereof, and the III-V material includes InAs, AlAs,GaAs, InP, AlP, GaP, InSb, AlSb, GaSb, or an alloy thereof.

In an embodiment, the II-VI material includes CdZnSe; and the III-Vmaterial includes InAs, AlAs, GaAs, InP, AlP, GaP, InSb, AlSb, GaSb, oran alloy thereof. In an embodiment, the II-VI material includesCdMgZnSe; and the III-V material includes InAs, AlAs, GaAs, InP, AlP,GaP, InSb, AlSb, GaSb, or an alloy thereof. In an embodiment, the II-VImaterial includes BeZnTe; and the III-V material includes InAs, AlAs,GaAs, InP, AlP, GaP, InSb, AlSb, GaSb, or an alloy thereof. In anembodiment, the II-VI material includes BeMgZnTe; and the III-V materialincludes InAs, AlAs, GaAs, InP, AlP, GaP, InSb, AlSb, GaSb, or an alloythereof.

In an embodiment, the II-VI material includes ZnSe, CdSe, BeSe, MgSe,ZnTe, CdTe, BeTe, MgTe, ZnS, CdS, BeS, MgS, or an alloy thereof, and theIII-V material includes InAs or an alloy thereof. In an embodiment, theII-VI material includes ZnSe, CdSe, BeSe, MgSe, ZnTe, CdTe, BeTe, MgTe,ZnS, CdS, BeS, MgS, or an alloy thereof, and the III-V material includesAlAs or an alloy thereof. In an embodiment, the II-VI material includesZnSe, CdSe, BeSe, MgSe, ZnTe, CdTe, BeTe, MgTe, ZnS, CdS, BeS, MgS, oran alloy thereof, and the III-V material includes GaAs or an alloythereof. In an embodiment, the II-VI material includes ZnSe, CdSe, BeSe,MgSe, ZnTe, CdTe, BeTe, MgTe, ZnS, CdS, BeS, MgS, or an alloy thereof,and the III-V material includes InP or an alloy thereof. In anembodiment, the II-VI material includes ZnSe, CdSe, BeSe, MgSe, ZnTe,CdTe, BeTe, MgTe, ZnS, CdS, BeS, MgS, or an alloy thereof, and the III-Vmaterial includes AlP or an alloy thereof. In an embodiment, the II-VImaterial includes ZnSe, CdSe, BeSe, MgSe, ZnTe, CdTe, BeTe, MgTe, ZnS,CdS, BeS, MgS, or an alloy thereof, and the III-V material includes GaPor an alloy thereof. In an embodiment, the II-VI material includes ZnSe,CdSe, BeSe, MgSe, ZnTe, CdTe, BeTe, MgTe, ZnS, CdS, BeS, MgS, or analloy thereof, and the III-V material includes InSb or an alloy thereof.In an embodiment, the II-VI material includes ZnSe, CdSe, BeSe, MgSe,ZnTe, CdTe, BeTe, MgTe, ZnS, CdS, BeS, MgS, or an alloy thereof, and theIII-V material includes AlSb or an alloy thereof. In an embodiment, theII-VI material includes ZnSe, CdSe, BeSe, MgSe, ZnTe, CdTe, BeTe, MgTe,ZnS, CdS, BeS, MgS, or an alloy thereof, and the III-V material includesGaSb or an alloy thereof

In an embodiment, the II-VI material includes ZnSe, CdSe, BeSe, MgSe,ZnTe, CdTe, BeTe, MgTe, ZnS, CdS, BeS, MgS, or an alloy thereof, and theIII-V material includes InAlAs. In an embodiment, the II-VI materialincludes ZnSe, CdSe, BeSe, MgSe, ZnTe, CdTe, BeTe, MgTe, ZnS, CdS, BeS,MgS, or an alloy thereof, and the III-V material includes GaInAs. In anembodiment, the II-VI material includes ZnSe, CdSe, BeSe, MgSe, ZnTe,CdTe, BeTe, MgTe, ZnS, CdS, BeS, MgS, or an alloy thereof, and the III-Vmaterial includes AlInGaAs. In an embodiment, the II-VI materialincludes ZnSe, CdSe, BeSe, MgSe, ZnTe, CdTe, BeTe, MgTe, ZnS, CdS, BeS,MgS, or an alloy thereof, and the III-V material includes GaInAsP.

Any suitable InP substrate may be used in the practice of the presentinvention. The InP substrate may be n-doped, p-doped, orsemi-insulating, which may be achieved by any suitable method or byinclusion of any suitable dopant.

In one embodiment of the layered construction according to the presentinvention, at least one of the alternating layers of II-VI and III-Vmaterials is in direct contact with the InP substrate. In an alternateembodiment, additional layers are interposed between the alternatinglayers of II-VI and III-V materials and the InP substrate. Whereadditional layers are interposed between the alternating layers of II-VIand III-V materials and the InP substrate, they may comprise anysuitable layers. Typically, these interposed layers are lattice-matchedor pseudomorphic to the InP substrate. The interposed layers may includeelements of a VCSEL, such as electrical contact layers, buffer layers,optical waveguide layers, active layers, quantum well layers, currentspreading layers, cladding layers, barrier layers, and the like. Theinterposed layers may include elements of a photodetector, such aselectrical contact layers, cladding layers, absorption layers, bufferlayers, and the like.

The layers of II-VI and III-V material may have any suitable thickness.The layers of II-VI and III-V material may have thicknesses,individually or on average, of between 0.1 nm and 10,000 nm, moretypically between 10 and 1,000 nm, more typically between 50 nm and 500nm, and more typically between 100 nm and 200 nm.

In one embodiment, the layered construction forms one or moredistributed Bragg reflectors (DBR's). The layered construction formingthe DBR may include any suitable number of pairs of II-VI and III-Vmaterials, from 2 to a very large number. In one embodiment, the layeredconstruction possesses sufficient reflectivity such that a DBR can bemade with no more than 20 pairs of layers of II-VI and III-V materials,more typically no more than 15 pairs, more typically no more than 12pairs, more typically no more than 10 pairs. In other embodiments, thelayered construction possesses sufficient reflectivity that a suitablyeffective DBR can be make with no more than 8 pairs, and more typicallyno more than 5 pairs.

In a DBR, the layer thickness is a quarter of the wavelength of thelight in that material:

$t = \frac{\lambda}{4n}$where t is the thickness of the layer, λ is the wavelength of the light,n is the refractive index of the material. Take as an example a DBRmirror according to the present invention comprisingCd_(0.52)Zn_(0.48)Se and In_(0.52)Al_(0.48)As layers that is designed tohave peak reflectivity at a wavelength of 1.55 μm. The refractive indexof Cd_(0.52)Zn_(0.48)Se at 1.55 μm is 2.49, and so the thickness of theCd_(0.52)Zn_(0.48)Se layer should be 156 nm. The refractive index ofIn_(0.52)Al_(0.48)As at 1.55 μm is 3.21, and so the thickness of theIn_(0.52)Al_(0.48)As layer should be 121 nm. In one embodiment, thelayered construction forms one or more distributed Bragg reflectors(DBR's) that have a maximum reflectivity that occurs at a wavelength inthe range of 1–2 microns.

In one embodiment, the layered construction forms one or moredistributed Bragg reflectors (DBR's) which form a part of a laser, suchas a VCSEL. The VCSEL may operate at any suitable wavelength. In oneembodiment, the VCSEL operates at a wavelength of between 1 μm and 2 μm,a range which provides for reduced dispersion and attenuation duringtransmission through optical fibers. Typically the VCSEL operates atwavelengths where optical fiber networks operate, typically around 1.3μm or 1.55 μm.

In one embodiment, the layered construction forms one or moredistributed Bragg reflectors (DBR's) which form a part of aphotodetector. The photodetector may be used in telecommunications,where it may be capable of optical-to-electronic conversion of gigahertzfrequency signals. Typical photodetectors work by absorption of opticalenergy and related generation of carriers, transportation of thephotogenerated carriers across the absorption region, and collection ofthe carriers with generation of a photocurrent.

FIG. 5 shows the basic components of a photodetector 90 utilizing theinventive layered construction 93 in which the other components shownare: DBR portion 91; electrical contacts 96 and 97 and mirror 98.

The layered construction according to the present invention may bemanufactured by any suitable method, which may include molecular beamepitaxy, chemical vapor deposition, liquid phase epitaxy and vapor phaseepitaxy. Typically, the layered construction according to the presentinvention may be manufactured without wafer fusion.

This invention is useful in opto-electronic technology, includingopto-electronic communications technology.

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention.

EXAMPLES Example 1

DBR Formation

A Distributed Bragg Reflector (DBR) mirror having 2 pairs of alternatinglayers of II-VI and III-V epitaxial semiconductor materials was grown onan InP substrate. The resulting structure is illustrated schematicallyin FIG. 1, and includes InP substrate 10, InAlAs buffer layer 20, firstCdZnSe layer 30, first InAlAs layer 40, second CdZnSe layer 50, secondInAlAs layer 60, and InGaAs cap layer 70. CdZnSe layers 30 and 50 andInAlAs layers 40 and 60 make up DBR 80. The II-VI material wasCd_(0.52)Zn_(0.48)Se that was n-type doped with Cl. The III-V materialwas In_(0.52)Al_(0.48)As that was n-type doped with Si.

The mirror was designed to have a peak reflectivity at 1.55 μm. For thatreason, the nominal values of InAlAs and CdZnSe layer thickness were 121nm and 156 nm, respectively.

The apparatus used was a Perkin-Elmer 430 solid source molecular beamepitaxy (MBE) system. The system includes two growth chambers connectedby an ultra-high vacuum transfer tube, one of which was used forAs-based III-V materials and the other for II-VI materials. The waferwas transferred back and forth between the two chambers for applicationof different layers via the ultra-high vacuum pipeline.

A (100)-oriented n-type, S-doped InP substrate was deoxidized in theIII-V chamber at 565° C. under As overpressure. A 120 nm-thick InAlAsbuffer layer was then grown at 540° C. using as deposition sources: anIn effusion cell, an Al effusion cell and an As valved cracker cell.After buffer growth, the wafer was transferred to the II-VI chamber forgrowth of the first CdZnSe layer. The growth was initiated by a 15minute Zn exposure at 185° C. and then a thin Cl-doped CdZnSe layer wasgrown at 200° C. by migration enhanced epitaxy (MEE). The substratetemperature was then ramped up to 270° C. and the remainder of theCl-doped CdZnSe layer was grown, to a thickness of 156 nm. After CdZnSegrowth, the sample was transferred back to the III-V chamber. A 5nm-thick Si-doped InAlAs capping layer was grown at 300° C. in order toreduce the loss of any constituents of the CdZnSe layer during thehigh-temperature InAlAs growth. The remainder of the 121 nm-thickSi-doped InAlAs layer was then grown at 540° C., thus forming the firstCdZnSe/InAlAs mirror pair. A second mirror pair was grown under the samegrowth conditions as the first pair. Finally, a 5 nm-thick n-InGaAs caplayer was grown on top of the structure, composed ofIn_(0.53)Ga_(0.47)As that was n-type doped with Si.

X-ray Diffraction

X-ray diffraction (XRD) performed on calibration samples using a Bedescientific QC1a double-crystal diffractometer confirmed that thecompositions of InAlAs and CdZnSe layers on InP substrates werelattice-matched. Two separate calibration samples were grown: CdZnSe onInP substrate and InAlAs on InP substrate.

Sem

The DBR mirror made as described above was cross-sectioned and examinedunder a Hitachi S4700 scanning electron microscope (SEM). FIG. 2 is ascanning electron micrograph of that sample. The micrograph shows InPsubstrate 10, InAlAs buffer layer 20, first CdZnSe layer 30, firstInAlAs layer 40, second CdZnSe layer 50, second InAlAs layer 60, andInGaAs cap layer 70. The micrograph shows thickness values for CdZnSeand InAlAs layers of approximately 142 nm and 116 nm respectively,somewhat thinner than the intended values.

Reflectivity

The reflectivity of the DBR mirror made as described above was measuredusing a Perkin-Elmer Lambda 900 UV/VIS/NIR spectrometer. The resultingdata are presented in FIG. 3, trace A. For the 2-pair CdZnSe/InAlAs DBRmirror, the peak reflectivity was 66% at 1.45 μm. The mirrorreflectivity was simulated based on transfer-matrix calculation by usingthe thickness values from SEM. (For more on the transfer-matrixcalculation please see: Theodor Tamir (ed.), “Guided-WaveOptoelectroncs,” 2nd Edition, Springer-Verlag). As evident in FIG. 3,the simulated curve (FIG. 3, trace B) fit the experimental data well.FIG. 3 also shows the simulated reflectivity as a function of wavelengthfor two comparative III-V/III-V DBR's: a 2-pair InGaAsP/InP (trace C)and a 2-pair AlGaAsSb/AlAsSb DBR (trace D). The reflectivity is only 46%for the 2-pair AlGaAsSb/AlAsSb DBR mirror and 40% for the 2-pairInGaAsP/InP mirror. The DBR according to the present inventiondemonstrates greatly improved reflectivity in comparison to currentlyavailable long wavelength DBR's of comparable thickness. Extrapolationfrom this data indicates that a DBR with a reflectivity of 95% can beachieved with 15 or fewer layer pairs.

Example 2

Growth of AlInAs/BeZnTe/AlInAs on InP

A (001) InP substrate wafer was transferred into an ultra-high vacuum(UHV) molecular beam epitaxy (MBE) chamber equipped with an As valvedcracker cell, and Al and In Knudsen effusion cells. The InP substratewas heated under an As-overpressure until the native oxide was desorbed.The oxide desorption temperature, as measured by an optical pyrometer,was approximately 560° C. The reflection high energy electrondiffraction (RHEED) pattern, at the time of oxide off, changed from(1×1) to (2×4), indicative of a Group V-terminated surface.

After the RHEED pattern transition to (2×4), the substrate temperaturewas reduced to between 500° C. and 530° C. for the growth of nominallylattice-matched AlInAs. The growth of the AlInAs was at a rate ofapproximately 1 μm/hr, under an As-rich V-ITT flux ratio.

After growth of an AlInAs layer, the substrate temperature was reduced,under an As overpressure, to less than 300° C. to form an excess-Assurface. At this time, the substrate was transferred out of the firstMBE chamber, and through a UHV pipeline to a second MBE equipped withBe, Zn, and Te Knudsen effusion cells.

Upon transfer into the second MBE chamber, the substrate was heated to atemperature at which the excess As is desorbed (approximately 360° C.),leaving an As-terminated surface which exhibits a (2×4) RHEED pattern.In this chamber, the temperature was measured indirectly by analyzingthe transmission spectrum of the substrate heater radiation through theInP substrate. The temperature-dependence of the bandgap of InP, andthus the absorption edge of the spectrum, were known.

After the AlInAs RHEED transition to (2×4), the substrate was cooled toapproximately 300° C., at which time the growth of nominallylattice-matched BeZnTe was commenced. The growth of BeZnTe was at a rateof approximately 0.8 μm/hr under a Te-rich VI-II flux ratio, whichexhibits a (2×1) RHEED pattern.

After the growth of the BeZnTe layer the substrate was removed from thesecond MBE chamber, and transferred via the UHV pipeline back to thefirst MBE chamber. Upon transfer into the first MBE chamber, thesubstrate was heated to the AlInAs growth temperature (between 500° C.and 530° C.). At an intermediate temperature, between 350° C. and 450°C., the BeZnTe surface was exposed to an As flux. When the substratetemperature reached the AlInAs growth temperature, a second layer ofAlInAs was grown, at the same rate and source fluxes as the first AlInAslayer.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand principles of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth hereinabove.

1. A layered construction comprising: an InP substrate; and alternatinglayers of II-VI and III-V materials; the materials of the alternatinglayers being selected from the following II-VI material comprisingBeZnTe or BeMgZnTe and III-V material comprising In_(y)Al_(1−y)As inwhich y is between 0.47 and 0.57; II-VI material comprisingCd_(x)Zn_(1−x)Se in which x is between 0.47 and 0.57 and the III-Vmaterial comprising InAlAs or AllnGaAs; or II-VI material comprisingZnSeTe and the III-V material comprising InAlAs or AlInGaAs.
 2. Thelayered construction according to claim 1 wherein said alternatinglayers of II-VI and III-V materials are lattice-matched to said InPsubstrate or pseudomorphic to said InP substrate.
 3. The layeredconstruction according to claim 1 wherein at least one of saidalternating layers of II-VI and III-V materials is in direct contactwith said InP substrate.
 4. The layered construction according to claim1 additionally comprising layers interposed between said InP substrateand said alternating layers of II-VI and III-V materials.
 5. The layeredconstruction according to claim 1 wherein said alternating layers ofII-VI and III-V materials form one or more distributed Bragg reflectors(DBR's).
 6. The layered construction according to claim 5 wherein saiddistributed Bragg reflector (DBR) has a maximum reflectivity that occursat a wavelength in the range of 1–2 microns.
 7. The layered constructionaccording to claim 5 wherein each DBR includes no more than 15 pairs ofalternating layers of II-VI and III-V materials and has a reflectivityof 95% or greater.
 8. The layered construction according to claim 1wherein the II-VI material comprises BeZnTe or BeMgZnTe and the III-Vmaterial comprises In_(y)Al_(1−y)As in which y is between 0.47 and 0.57.9. The layered construction according to claim 1 wherein the II-VImaterial comprises Cd_(x)Zn_(1−x)Se in which x is between 0.47 and 0.57and the III-V material comprises InAlAs or AlInGaAs.
 10. The layeredconstruction according to claim 1 wherein the II-VI material comprisesZnSeTe and the III-V material comprises InAlAs or AlInGaAs.
 11. Thelayered construction according to claim 1 wherein said layers of II-VIand III-V material have an average thickness of between about 100 nm andabout 200 nm.
 12. A laser comprising the layered construction accordingto claim
 1. 13. A photodetector comprising the layered constructionaccording to claim 1.